Well being a mining engineer, I created a software that would give you the blasting patterns based on the parameters that were input like the rock condition, vibration levels, flyrock, required output etc.
The program even showed a glimpse of what the face would look like after blasting and it gave us both elevation as well as the side view of the face. Also gave the estimate of amount of explosives required and other theoritical reporting stuff.
Had a facility to be connected to a vibration monitor and could directly read the output of the same.
Has to be my best so far. But that was all in VB6.0.
Taking of .NET, I created a web.config editor application that also had the facilities of encryption in it.
--Ashutosh